The use of a smart grid connected renewable energy system has been regarded as our next-generation power grid for solving the energy crisis. The smart grid system transfers electrical power from a renewable energy source, like wind energy, and generates regulated power for industrial and domestic uses. However, the development of a smart grid presents many new challenges with respect to power quality [1]. In particular, reactive power has been a major issue. Large reactive power draws more reactive current which results in either an increase in the operating cost or a decrease in the transmission capacity. This necessitates various measures including the use of dynamic reactive power compensators to overcome the power quality issue.
Conventionally, a thyristor based static var compensator (SVC), comprising a fixed shunt capacitor in parallel with a thyristor-controlled reactor (FC-TCR), is used to control the firing angles of the thyristors and compensate for the reactive power [2]. However, during the operation of the FC-TCRs, low-order harmonic currents are generated, which can deteriorate system performance. This problem was particularly discussed by Haque et al. with no solution provided [3].
In order to address the problem of harmonic current injection static synchronous compensator (STATCOM) was developed to achieve better power stability. STATCOM is a voltage-source converter using an insulated-gate bipolar transistor (IGBT) or an integrated gate commutated thyristor (IGCT). This system has faster response and less harmonic current injection than SVC [4]. However, a STATCOM system is more expensive than SVC at the same VA power rating. Therefore, this topology failed to replace the older SVC technology.
Benton [5] and Zanotto et al. [6] suggested the use of a parallel combination of SVC and passive power filter (SVC+PPF) to reduce the harmonic current injection. However, the oscillating time and cost of this approach are both significantly higher. Subsequently, Luo et al. [7] proposed a combined system of the SVC and the STATCOM, which can eliminate harmonic current injection by the SVC and compensate for both the reactive power and harmonic current of the nonlinear load. However, considering the complexity of the system, the initial cost of this approach can be very high. In order to reduce the initial cost, Kulkami et al. [8] proposed an artificial neural network (ANN) approach to identify the optimum trigger angles for the thyristor controlled reactors and thyristor switched capacitors (TCR-TSC) with lowered harmonic current injection. However, as the firing angles are probably not matched with the required compensating reactive power, the TCR-TSC may sacrifice its reactive power compensation capability.
As a result, there is a need for a technique for compensating for dynamic reactive power in a power grid system by a thyristor controlled LC (TCLC) compensator that also mitigates harmonic current injection problem by the thyristor (during switching on or off) at a low cost.